1. Field of the Invention
This invention relates to a floating-type composite magnetic head and the production method thereof, more particularly, to a magnetic head wherein the magnetic gap depth is precisely controlled by inserting and molding a magnetic core provided with concave marks on its side surface into a slit provided in a slider.
2. Related Art
FIG. 4 shows an example of a magnetic core being used in a floating-type composite magnetic head. The magnetic core 41 comprises a C-shaped core 42 and an I-shaped core 43 joined together and bonded over a gap spacer so that a magnetic gap 44 is formed between them. The C-shaped core 42 and I-shaped core 43 are usually made of such materials as, for example, single crystal ferrite and, recently, in order to meet increasing requirements for high density storage, it is usual to apply a high-permeability magnetic film such as Fe--Al--Si alloy film on the surfaces facing the magnetic gap of either one or both of the cores.
With the example as per FIG. 4, said high permeability magnetic films 45 and 46 are applied to both the C-shaped core and I-shaped core. In FIG. 4, numeral 47 represents the depth of the magnetic gap 44, or the distance between the magnetic core surface facing the storage medium and the apex (the point on the C-shaped core where the plane forming the magnetic gap intersects with the inclined plane, whereby the gap distance by the plane, formed between the C-shaped and I-shaped cores remains the same and whereby the gap distance by the inclined plane gradually increases, and the point is indicated by a point or line in the drawing). The dimensional preciseness of the depth of the magnetic gap has a significant influence on the reading and reproducing characteristics.
Consequently, strict control of the apex position is very important in the production of these magnetic heads. Meanwhile, numeral 48 stands for reinforcing glass which fills the space between the C-shaped core 42 and I-shaped core 43 to firmly join the cores together, the filler extending all the way to the end of the coil winding clearance 49.
FIG. 5 is a schematic diagram showing an example of the structure of a floating-type composite magnetic head. The slider 52 of this floating-type composite magnetic head 51 is equipped with air bearings 53a and 53b to float on the magnetic disc (omitted from the drawing) functioning as the magnetic storage medium at both ends of its plane which faces the magnetic disc, air bearing 53a of the air bearings being equipped with a slit 54. The slit 54 is usually provided on the trailing side off the storage medium (which can be referred to as the air outlet side). A magnetic core 55 is inserted into the slit 54 and molded using glass filler 56. Numeral 57 represents a slot which is formed so that the coil winding clearance 58 maintained after molding the magnetic core 55.
A floating-type composite magnetic head of the structure is being produced under, for example, the method given below. FIG. 6 is an elevation of a floating-type composite magnetic head viewed from the slotted end. The exemplified production method includes inserting the magnetic core 61 into the slit 64 and placing a glass rod over the air-bearing side of the slit before heating the glass rod to melt it under a vacuum atmosphere or an ambient atmosphere of argon (Ar) or nitrogen (N.sub.2), thus filling the space between the slit 64 and magnetic core 61 with glass filler 65 which molds the magnetic core 61.
After molding the magnetic core in the above-mentioned manner, excess glass filler is removed and the air-bearings 62a and 62b are subjected to a finishing process to obtain the required depth of the magnetic gap to complete a floating-type composite magnetic head.
When applying the finishing process to the air bearings, the magnetic gap depth has thus been controlled by observing and measuring the apex using an optical microscope and a micro-measurement scale, etc. installed to the eyepiece section. When doing this, since the magnetic core is buried under the glass filler for molding inside the slit as aforementioned it is impossible to directly view the apex of the magnetic gap from the direction perpendicular to the side surface of the magnetic core (for example, the direction of arrow A in FIG. 6). Consequently, the apex is measured by observing it from an inclined direction (for example, the direction of arrow B in FIG. 6) across the glass filler by tilting the magnetic head or the optical microscope.
Nevertheless, in the aforementioned method, since the focal distances to different points along the ridge of the magnetic core differ and the image of the edge line of the magnetic core appears indistinct owing to the inclined observation, it becomes necessary to maintain a larger distance between the objective lens and the magnetic head to obtain a clearer view which in turn limits the task to highly skilled workers because of the restriction to the use of higher magnification. Also, with the aforementioned method wherein inclined measurement is carried out across the glass filler, the measurement reading of the magnetic gap depth may be smaller than the actual dimension owing to the fact that the refractive index of glass is larger than that of air, and scratches applied to the surface of the glass filler while processing the air bearings interfere with the precise measurement of the apex point, thus making it extremely difficult to initiate commercial mass production under high precision control of the gap depth. Furthermore, when a housing made of ferrite is employed, the dark coloring of the housing hinders a view of the gap depth.
One possible solution to this problem is to provide a mark on the magnetic core which can be used as a reference for the magnetic gap depth and to measure the mark to determine the magnetic gap depth indirectly rather than by performing direct measurement of the magnetic gap depth (in other words, the apex position).
This method is already a known production method of thin-film magnetic heads wherein, for example, a triangular-pattern mark 91 in FIG. 9 whose width varies in the direction of the magnetic gap depth having one of its apexes positioned level with the apex of the magnetic gap and a rectangular-pattern mark 92 having one of its sides positioned level with the apex of the magnetic gap are applied by a thin-film forming process. When grinding the air bearing, the width of the triangular pattern x.sub.2 is measured and is then compensated on the basis of the measurement result of the rectangular pattern width x.sub.4 thus making an indirect measurement of the magnetic gap depth x.sub.3. (Refer to Japanese Patent Laid-Open No. 49212/1990.)
Nevertheless, marks are applied by the thin-film forming process peculiar to thin-film magnetic heads, whereas floating-type composite magnetic heads which do not include the thin-film forming process in their production, are not at all applicable to this method.
To solve this problem, Japanese Patent Laid-Open No. 121105/1990 suggests measuring the magnetic gap depth using reference marks on a floating-type composite magnetic head by a marking method entirely different from that for the thin-film magnetic heads.
FIGS. 7 and 8 illustrate the said suggestion. To form the magnetic core block 71 first, preparing a pair of ferrite wafers 73 and 74, their contact planes 73a and 74a are mirror-finished. On said contact planes 73a and 74a, preprocessing grooves 73b and 74b are provided at a fixed pitch P. Further, on the contact plane 74a of the second wafer 74, a coil winding clearance groove 72 is provided in the direction perpendicular to the preprocessing grooves 74b, 74b . . . and on the contact plane 73a and the opposite surface of the first wafer 73, a glass filler groove 76 and notch groove 75 are provided respectively in the direction perpendicular to the preprocessing grooves 73b, 73b, . . . . Subsequently, gap spacer layers made of a material such as SiO.sub.2 are applied to respective contact planes 73a and 74a by deposition before joining the contact planes of first and second wafers 73 and 74. Then, glass rods 79, 78 and 77 are inserted into the preprocessing grooves 73b and 74b, glass filler groove 76 and notch groove 75, respectively, before heating and melting said glass rods to fix the first and second wafers 73 and 74 by molding the preprocessing grooves 73b and 74b and the glass filler groove 76, and to fill the notch groove 75 with glass filler.
The molded block thus formed is then cut along the dotted lines as given in FIG. 7 and the cut-out blank is then kerf-machined to form the disc facing part of track width t to complete the core block. The core block is further sliced to form magnetic core 81 of the structure indicated in FIG. 8. Meanwhile, the magnetic gap 84 is formed along the contact planes of the first and second wafers across the disc facing part.
Magnetic core 81 thus obtained is provided with a measuring mark 85 at a prescribed position, corresponding to the apex, on its exposing external side 83. After the core is inserted and cemented in the slit, indirect measurement of the magnetic gap depth can be accomplished by measuring the mark which can be viewed directly from outside.
In recent years, demands for high density storage have been increasing and, simultaneously, the magnetic gap depth of floating-type composite magnetic heads is becoming smaller and smaller thus requiring stricter dimensional precision in relation to nominal dimensions.
Under such situation, with the aforementioned method whereby the mark is machined onto the exposed external side of the core, issues hitherto neglected are being highlighted, such as the positional accuracy of machining being difficult to obtain because the distance between the apex point and the mark is comparatively large, or only a slight incline of the magnetic core cemented in the slit resulting in a serious error.
Furthermore, since the mark is made on the core block before slicing into magnetic cores, it is comparatively difficult to place the mark at the position which accurately corresponds to the apex with all the magnetic cores thus produced owing to dislocation occurring when cemented, thus making it necessary to measure the position of the apex and the mark with each magnetic core before grinding the air bearings on the basis of the respective measurement results. Therefore, it is necessary to classify magnetic cores according to grinding amount, making mass-production difficult.